The invention relates to improvements in piston engines (also known as reciprocating or displacement engines), and more particularly to improvements in methods of and means for preventing or reducing the extent and/or frequency of stray movements of crankshafts in such engines. Still more particularly, the invention relates to improvements in the construction and mounting of vibration dampers for the crankshafts of piston engines.
Published German patent application Ser. No. 195 19 261 discloses a torsional vibration damper which comprises an annular casing adapted to be connected to the shaft of a machine and confining a flywheel which is rotatable relative to the casing against the opposition of a body of viscous fluid. This published application proposes to position the casing of the vibration damper at the front end face of, and to fasten the casing to, the front end (snout) of the crankshaft. A drawback of such proposal is that the thus attached damper occupies a substantial amount of space which is not always available under the hoods of certain types of motor vehicles (such as compact cars), especially if the engine is installed transversely of the direction of forward movement of the conveyance.
Published German patent application Ser. No. 40 25 848 discloses a modified vibration damper which is intended for use in piston engines and employs annular flywheels as well as a hub which is to be secured to the crankshaft of the engine. The annular flywheels are movably secured to the hub by buffers of rubber or other suitable elastomeric material. The hub is provided with or carries a pulley for one or more endless belts serving to transmit motion to the camshaft of the engine and/or to one or more auxiliary aggregates of the motor vehicle.
One of the purposes of vibration dampers for the crankshafts of piston engines is to suppress the characteristic frequencies (harmonic vibrations) of the crankshafts. In many instances, the characteristic frequency of the crankshaft in the housing of a piston engine is in the range of between 300 and 450 Hz. Such frequency is induced primarily as a result of iregularities attributable to compression and expansion that take place in the cylinders for the pistons of the engine. Vibrations at the torsional resonancy can result in breakage of the crankshaft, and this is the reason that the crankshafts of piston engines are normally equipped with vibration dampers (e.g., in the form of heavy, rubber-mounted wheels in front of the crankshaft) to counter harmonic vibrations.
In order to achieve a satisfactory vibration damping action, the vibration damping frequency must be selected with a rather high degree of accuracy. As already mentioned above, presently known attempts at adequate damping of vibrations of a crankshaft in a piston engine include the provision of at least one annular flywheel which is movably connected to a hub or another input element of the vibration damper by a buffer of rubber (or other energy-storing elastomeric material), or by a body of oil or another suitable viscous fluid.
In addition to their often excessive space requirements, the aforediscussed presently known vibration dampers for the crankshafts of piston engines exhibit the drawback that the viscosity of fluid can be greatly influenced by changes of temperature and that such temperature changes can also exert an undue influence upon the spring gradient of the elastomeric material. It is to be borne in mind that a vibration damper for the crankshaft of a piston engine is installed in immediate or very close proximity to one or more sources of pronounced heat. Attempts to overcome or to reduce the undesirable influence of elevated temperatures upon the predictability and reliability of operation of conventional vibration dampers for crankshafts include the utilization of oversized vibration damping masses to thus widen the frequency range within which the damper is or should be effective. However, the utilization of oversized masses brings about other serious problems and drawbacks such as a greatly increased fuel consumption and an increased resistance of rotary components of the piston engine to the setting in rotary motion.
An object of the invention is to provide a vibration damper which can be utilized with the crankshaft of a piston engine and is less affected by temperature changes and/or elevated temperatures than heretofore known vibration dampers for crankshafts.
Another object of the invention is to provide a vibration damper which can stand pronounced thermal stresses for exended periods of time.
A further object of the invention is to provide a vibration damper which is constructed and assembled and which can be installed in a piston engine in such a way that it can effectively counter harmonic vibrations of a crankshaft during each stage of operation of the piston engine.
An additional object of the invention is to provide a novel and improved crankshaft-vibration damper combination which is not affected, or not appreciably affected, by pronounced temperature changes and which can be utilized in lieu of and as a superior substitute for conventional crankshaft-vibration damper combinations.
Still another object of the invention is to provide a novel and improved method of assembling a piston engine wherein the crankshaft is prevented from carrying out any, or from carrying out excessive, harmonic vibrations.
A further object of the invention is to provide a novel and improved module which embodies a crankshaft and can be utilized in piston engines as a superior substitute for conventional crankshaft-vibration damper combinations.
Another object of the invention is to design a vibration damper for the crankshaft of a piston engine in such a way that the range of thermal influence upon the frequency range in which the vibration damper is effective is much narrower than in connection with the utilization of conventional vibration dampers for the crankshafts of piston engines.
An additional object of the invention is to provide a simple, compact and inexpensive but highly effective vibration damper which can be put to use in all or nearly all types of piston engines to oppose stray movements of the crankshaft.
Still another object of the invention is to provide a damper which can be readily installed in the housing of a piston engine.
A further object of the invention is to provide a piston engine which embodies one or more dampers of the above outlined character.
Another object of the invention is to provide a piston engine with a novel and improved housing for the crankshaft and for a damper which serves to counter-harmonic vibrations of the crankshaft.
An additional object of the invention is to provide a motor vehicle embodying a piston engine which utilizes the above outlined crankshaft-vibration damper combination.
Still another object of the invention is to provide a piston engine wherein the vibration damper for the crankshaft need not be provided with a discrete lubricating system.
One feature of the present invention resides in the provision of a piston engine which comprises a housing, a crankshaft which is rotatably journalled in the housing, and means for damping vibrations of the housing and the crankshaft relative to each other. The damping means is at least partially confined in the housing and is provided on the crankshaft.
In accordance with a presently preferred embodiment, the damping means is fully or practically fully confined in the housing of the piston engine.
A presently preferred embodiment of the damping means comprises a rotary input element and at least one rotary inertia-enhancing mass. The input element and the at least one mass are rotatable relative to each other, and the damping means further comprises energy storing resilient means interposed between the input element and the at least one mass to oppose rotation of the input element and the at least one mass relative to each other. The energy storing resilient means can comprise one or more coil springs, and the piston engine can further comprise at least one friction generating device which is installed to oppose at least certain stages of rotation of the input element and the at least one mass relative to each other.
It is possible to utilize the friction generating device(s) in lieu of the energy storing resilient element or elements.
The damping means can be mounted on or in or adjacent a cheek or web of the crankshaft. For example, the damping means can be located adjacent a cheek as seen in the axial direction of the crankshaft.
The damping means can include or constitute a ring which is concentric with a portion of the crankshaft, for example, with an end portion referred to as snout.
A cheek of the crankshaft can be positioned adjacent to but still spaced apart from a wall of the housing (as seen in the axial direction of the crankshaft), and the damping means can be disposed in the housing between such cheek and the wall. The crankshaft can comprise a portion (such as the aforementioned snout) which is rotatably mounted in the wall.
The aforementioned input element of the damping means is rotatable with the crankshaft; the input element can be fixed to the shaft by a suitable form-locking connection or permanently, e.g., by welding.
The damping means or the piston engine can further comprise means for limiting the magnitude of torque which the crankshaft can transmit to the input element of the damping means. For example, the torque limiting means can comprise one or more slip clutches.
The input element of the damping means can constitute a rotary annular body and the mass of the damping means can be designed and mounted in such a way that it is adjacent at least one side of the annular input element (as seen in the axial direction of the crankshaft). The mass and the input element are rotatable relative to each other against the opposition of the aforementioned resilient energy storing element or elements. If provided, a friction generating device can be installed to operate between the input element and the mass; such friction generating device can operate in parallel with the energy storing element(s).
If the mass comprises several discrete portions, e.g., two discrete portions, such discrete portions can be located at opposite sides of the annular input element of the damping means and can be spaced apart from each other in the axial direction of the crankshaft. Each energy storing element of the damping means is preferably installed in windows which are provided therefor in the input element and in at least one portion of the mass to oppose rotation of the input element and the at least one portion of the mass relative to each other. Such damping means preferably further comprises means (e.g., rivets) for non-rotatably connecting the portions of the mass to each other. As already mentioned hereinbefore, it is presently preferred to employ energy storing resilient elements in the form of coil springs, and each portion of the mass can but need not have an annular shape. If the just described embodiment of the damping means employs at least one friction generating device which serves to oppose rotation of the mass and the input element relative to each other (e.g., in parallel with the coil spring or springs), the friction generating device can comprise at least one energy storing member (e.g., a diaphragm spring or a corrugated washer-like spring) which reacts against the mass or against the input element and bears upon the input element or the mass.
The input element of the damping means can be provided with a tubular extension which surrounds an end portion of the crankshaft, such as the aforementioned snout. The extension is preferably located radially inwardly of the resilient energy storing element or elements of the damping means. It is possible to design the extension in such a way that it constitutes an axial and/or a radial bearing for the end portion of the crankshaft in the housing.
Another feature of the invention resides in the provision of a vibration damper which can be utilized in a piston engine having a housing and a crankshaft which is rotatable relative to the housing by one or more connecting rods receiving motion from pistons, and which serves to transmit torque to (or which constitutes) the rotary output element of the engine, e.g., an output element which can transmit torque to a friction clutch in the power train of a motor vehicle. The crankshaft and the vibration damper constitute a module which is ready to be rotatably mounted in the housing of the piston engine.
The damper can be designed in such a way that it includes a portion which surrounds an end portion of the crankshaft.
The input and output elements of the vibration damper forming part of the module can be immediately adjacent a cheek or web of the crankshaft.
Alternatively, a cheek of the crankshaft can be constituted (either entirely or in part) by the vibration damper of the module.
The damper can constitute an annular or a substantially U-shaped (such as horseshoe-shaped) structure.
The crankshaft can be designed in such a way that it includes a cheek and an oval or substantially oval portion adjacent the cheek. Such oval portion can extend radially of the rotational axis of the crankshaft and it can be flanked by two surfaces which are at least substantially normal to such axis. The damper has a substantially U-shaped outline, it surrounds the oval portion, and includes two legs which at least partially abut the cheek. Fastener means (e.g., bolts or screws) is provided to reliably connect the legs of the damper to the cheek; alternatively, the damper can be permanently affixed (e.g., welded) to the cheek.
A further feature of the invention resides in the provision of a method of assembling a piston engine wherein a crankshaft is rotatable in a housing and has a tendency to perform at times harmonic vibrations in actual use of the engine. The method comprises the steps of assembling the crankshaft and at least one vibration damper into a module, and thereupon rotatably mounting the crankshaft of the thus obtained module in the housing.
The assembling step can include incorporating the at least one vibration damper into a cheek of the crankshaft.
The assembling step can also include combining the crankshaft with a plurality of identical or different vibration dampers.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved vibration damper itself, however, both as to its construction and the modes of assembling, installing and utilizing the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.